The long-term objective of this research is to understand how organisms evolve at a molecular level. The short-term goal is to understand gonad development in the nematode Pristionchus pacificus. The nematode gonad is composed of somatic and germline tissues. To form a functional organ, the right number of cells must be made, the right cell types specified, and the cells must rearrange to form functional tissues in the correct location. The P. pacificus gonad has many morphological differences in comparison to the C. elegans gonad. Thus, investigation of P. pacificus gonad development offers the chance to study change in many processes. Over the next three years, the P. pacificus gonad will be characterized, and genes involved in gonad development will be isolated. Classical lineaging techniques and laser ablations are proving useful to fate map the gonad. Cell contacts are being described using electron micrographs. Concurrently, genetic screens are uncovering loci involved in gonad development. In depth study of a class of putative heterochronic genes that affect gonad developmental programs has begun. Comparisons with homologous C. elegans genes will begin to dissect how the processes that form the nematode gonad have changed.